In lawn care, groundskeeping and landscape care, there is a great need for plant or weed control without the application of herbicides or toxic substances.
Reducing the use of pesticides for weed and plant control has become an issue of national importance. Ground water is vitally important and the use of herbicides to prevent weeds from growing in homeowner and commercial lawns adversely impacts the quality of ground water. Most herbicides are persistent, soluble in water, and ingestion at high toxicity levels can be carcinogenic, affecting the human nervous system and causing endocrine disruption.
To protect water quality, simple removal methods not relying on pesticides are widely sought. Ninety-five percent of fresh water on earth is ground water. Ground water is found in natural rock formations called aquifers, and are a vital natural resource with many uses. Over 50% of the USA population relies on ground water as a source of drinking water, especially in rural areas.
In the USA, concerns about the potential impacts of herbicides on human health, as well as on terrestrial and aquatic ecosystems, have led to a wide range of monitoring and management programs by state and federal agencies, such as the U.S. Environmental Protection Agency (USEPA). For example, atrazine is a toxic, white, crystalline solid organic compound widely used as an herbicide for control of broadleaf and grassy weeds, and has been detected in concentrations problematic for human and animal health.
Mechanical and thermal phenomena marshaled against undesirable plants by prior art devices, methods and teachings are not effective overall, and this is due in large part to the natural robustness of plants, due to their physiology and responses to natural trauma. The role of repair, regrowth, and the beneficial effects of soil-borne microbes all play a role in the hardiness of plants to prior art thermal and mechanical methods for plant control.
Evaluation of effective methods for plant control using largely non-invasive phenomena is a difficult subject area to evaluate for general effectiveness because of many and varied biologic and environmental factors, including plant species, condition, type, environmental history, solar insolation, weather, and varied actions of insects, animals and microbiotica.
A key component for nearly all plants, including nuisance vegetation, is its root system. A typical root comprises various internal layers, including a xylem layer which operates essentially to transport water and provide, when needed, healing substances that repair wounds, such as burn wounds or severing, lacerations, and the like. Surrounding the xylem layer is a phloem layer, typically a living transport layer, which transports organic substances such as glucose and other sugars, amino acids and hormones. Surrounding phloem layer is a cortex, which is in turn surrounded by an epidermis, which acts like a skin which sheds dead cells.
In the immediate vicinity of the root of a plant, or on the root itself, is what is known as rhizospheric soil, which acts as a key root-soil interface of supreme importance for plant health. It is well known that soil-borne microbes interact with plant roots and soil constituents at this root-soil interface. This produces a dynamic environment of root-microbe interactions known as the rhizosphere, whose character and effect on the life of a plant varies widely with differing physical, chemical, and biological properties of the root-associated soil. Root-free soil without such organisms is known as bulk soil. Releasing of root exudates, such as epidermis flakes and other secretions, is sometimes called rhizodeposition and provides growth material, structural material or signals for root-associated microbiota. These microbiota feed on proteins and sugars released by roots. Protozoa and nematodes that feed on bacteria are also present in the rhizosphere, and provide nutrient cycling and disease suppression by warding off pathogens. [Ref: Oxford Journals Journal of Experimental Botany Volume 56, Number 417 Pp. 1761-1778, hereby incorporated in this disclosure in its entirety].
The balance of populations in a healthy symbiotic rhizosphere is important, because, in part, the bacteria which provide disease suppression interact with pathogens in a variety of ways, including mechanisms of antagonism, such as by competition for nutrients, parasitism, predation and antibiosis. Fungi, too, can be involved, and their actions, when turned from symbiotic to antagonistic, can be lethal for a plant.
There are three separate, but interacting, components recognized in the rhizosphere: the rhizospheric soil, the rhizoplane, and the root itself. The rhizosphere is soil influenced by roots via release of substances that affect microbial activity. The rhizoplane is the root surface, including the strongly adhering soil particles. The root itself also participates, because certain micro-organisms, known as endophytes, are able to colonize root tissues.
Any method to eradicate nuisance vegetation is typically influenced by the overall effect—and possible later influence—on the plant roots, and the rhizosheric soil. Interactions of a plant with electromagnetic radiation have been explored, but easy, safe, clean and efficient eradication meeting certain requirements has been heretofore elusive.
In this disclosure, the plant root crown, as discussed below, figures importantly.
In the prior art, basic thermal and mechanical techniques to eliminate nuisance vegetation are not sufficiently effective for use a commercially viable eradication program or system. This includes
[1] basic pulling of plant stems, roots, or other plant components to induce tensile failure, such as by natural events like feeding of cows and other ruminants;
[2] tensile failure below ground surface or soil grade;
[3] severing action or cut action, such as by gnawing or eating by an animal;
[4] cutting using a cutting tool or machine such as a chain saw;
[5] surface trauma delivered to plant root epidermis and cortex, such as lacerating or abrasion of the epidermis and possibly the cortex of a root, such as done by a gnawing animal, or by trauma delivered by a shovel blade or other tool; or
[6] needle wounds, which lend themselves to repair using latex or other healing substances that are dispatched to the scene of the wound, often originating from the xylem layer to transport needed enzymes and healing tars.
Biological responses to unnatural illumination can be counter-intuitive and complex, and there are many phenomenological findings discovered.
Now referring to FIG. 1, a schematic representation of a general electromagnetic spectrum for wavelengths of radiation of significance that are potentially incident upon a plant, with wavelengths ranging from 1 mm to less than 100 nm is shown. In the infrared portion, or heat radiation portion of the electromagnetic spectrum, the near-infrared, or near-IR, as it is commonly known, ranges in wavelength from 700 nm to 3 microns. Visible light is generally taken to range from 700 nm to 400 nm. Ultraviolet radiation is generally taken to be of wavelength less than 400 nm, with near-ultraviolet further divided into known portions UV-A (400−320 nm), UV-B (320−280 nm) and UV-C (280 nm−100 nm), which is extremely dangerous for humans and is often used as a germicidal radiation to purify water and kill bacteria, viruses, and other organisms.
Now referring to FIG. 2, a cartesian plot of both unfiltered solar radiation and net (ground) solar radiation is shown, with spectral radiance in watts per square meter per nanometer versus wavelength in nanometers (nm) is shown. Photosynthesis in plants makes use of visible light, especially blue and red visible light, and ultraviolet light, to varying degrees, depending on a host of factors including plant species and type, radiation exposure history and other factors. Approximately seven percent of the electromagnetic radiation emitted from the sun is in a UV range of about 200-400 nm wavelengths. As the solar radiation passes through the atmosphere, ultraviolet or UV radiation flux is reduced, allowing that UV-C (“shortwave”) radiation (200-280 nm) is completely absorbed by atmospheric gases, while much of the UV-B radiation (280-320 nm) is additionally absorbed by stratospheric ozone, with a small amount transmitted to the Earth's surface. Solar UV-A radiation (320-400 nm) is essentially, for practical purposes, not absorbed by the ozone layer.
Plants tend to respond to UV-B irradiation by stimulating protection mechanisms or by activating repair mechanisms to reduce injury and perform repair.
A common protective mechanism against potentially damaging irradiation is the biosynthesis of UV absorbing compounds, which include secondary metabolites, mainly phenolic compounds, flavonoids, and hydroxycinnamate esters that accumulate in the vacuoles of epidermal cells in response to UV-B irradiation. These compounds attenuate UV-B range radiation and protect the inner or deeper cell layers, with little absorptive effect on visible light.
UV-B radiation is considered highly mutagenic, with plant DNA particularly sensitive. UV-B radiation causes phototransformations and can result in production of cyclobutane pyrimidine dimers (CPDs) and pyrimidine (6-4) pyrimidinone dimers (6-4 Pps). DNA and RNA polymerases are generally not able to read through these photoproducts and the elimination of these cytotoxic compounds is essential for DNA replication and transcription and for plant survival. (Britt and May, 2003). To cope, most plants have developed repair mechanisms including photoreactivation, excision, and recombination repair. Photoreactivation is a light-dependent enzymatic process using UV-A and blue light to monomerize pyrimidine dimers: Photolyase binds to the photoproducts and then uses light energy to initiate electron transfer to break the chemical bonds of the cyclobutane ring and restore integrity of the bases.
It is now known that plant roots also are simply generally sensitive to UV-B light levels, such as via the action of the gene RUS1, and can pass this information on to other parts of a plant responsible for growth and development. Low dosages of UV-B light can provide important signals to the rest of the plant and can be beneficial to plant growth, helping young plants develop in a timely way, and helping promote seedling morphogenesis. For long term exposure of weeks' duration, too much UV-B light can be toxic to some plants. However, any resulting lethality is not suited for meeting the purposes served by the instant invention, as discussed below.
The allelopathic behavior of plants can be influenced by exposure to added (artificial) UV-B radiation [ref: “Allelopathic Influence of Houndstongue (Cynoglossum officinale) and Its Modification by UV-B Radiation,” Nancy H. Furness, Barbara Adomas, Qiujie Dai, Shixin Li, and Mahesh K. Upadhyaya; Weed Technology 2008 22:101-107].
Importantly, UV-B radiation can trigger biochemical steps to activate internals processes such as wax production to provide a plant with protection against further ultraviolet radiation [ref: “A UV-B-specific signaling component orchestrates plant UV protection,” Brown B A, Cloix C, Jiang G H, Kaiserli E, Herzyk P, Kliebenstein D J, Jenkins G I; Proc Natl Acad Sci USA. 2005 Dec. 13; 102(50):18225-30. Epub 2005 Dec. 5]. Plant epidermal flavonoids can protect the photosynthetic apparatus from UVB-mediated damage [ref: “Protection of the D1 photosystem II reaction center protein from degradation in ultraviolet radiation following adaptation of Brassica napus L. to growth in ultraviolet-B,” Wilson, M. I. and B. M. Greenberg (1993) Photochem. Photobiol. 57, 556-563] [ref: “A flavonoid mutant of barley (Hordeum vulgare L.) exhibits increased sensitivity to UV-B radiation in the primary leaf,” Reuber, S., J. F. Bornman and G. Weissenbo″ck (1996) Plant Cell Environ. 19, 593-601].
Now referring to FIG. 3, a partial schematic representation of a class of prior art plant eradication using various large infrared radiative transfers is shown. A plant Y with root R is shown receiving a large infrared radiative transfer from a forest fire, or any number of prior art infrared radiation-producing processes listed as shown, such as via a flame, an incandescent body, a hot gas, vapor (e.g., steam) or fluid, or via contact with a hot body, or via exposure to known IR or infrared radiators.
Because of the their inherited ability to withstand forest fires and lightning strikes, most plants do not respond in large numbers to application of heat as given in the prior art. Application of thermal contactors or applicators have not met with success. The heat thus delivered is ineffective or can be beneficial or stimulative, with any resultant subsequent repair to a root often making the root more robust to future thermal trauma.
Application of thermal energy and high doses of radiant energy have been shown in the prior art to burn, incinerate, discolor, or render useless above-ground plant components. Whether or not those same plants grew back, however, is often left unstated in prior art disclosures.
FIG. 3, which shows schematically as an example a FIRE impinging upon plant Y and/or root R, is followed by FIG. 4 showing a burned root with a burned stump as shown, such as might be found after a forest fire, with combustion byproducts, volatilized proteins or smoke 88 rising from the stump as shown. Even obliterating plant Y above ground in this manner typically results in the response shown in FIG. 5, which shows Regrowth as shown.
It is not sufficient merely to damage certain components of a plant, such as above-surface foliage. While visible above-ground damage may be desirable for an operator of a eradication machine, actual lethality can be short of expectations and short of what is required for a successful eradication system.
For example, prior art U.S. Pat. No. 5,189,832 to Hoek et al., discloses gas-fired burners which are directed at nuisance vegetation along a ground plane. This and other prior art methods which burn or heat plant parts usually fail, because plants have evolved to tolerate—and sometimes be stimulated by, forest fires and lightning strikes.
Similarly, when propane and heated ceramics burn off foliage, root structure remains among plants, and many plants regrow. Soil is an excellent thermal insulator both because of the presence of what are essentially refractory materials such as silica, sand, igneous rock particles, and the like—and also because of air content, moisture content, and because of its thermal mass.
It has been found through experimentation that It takes approximately one hour for a 8000 btu/hour output propane torch to have significant thermal effects 2.5 cm into bulk soil. Common nuisance vegetation such as Digitaris sanguinalis in the crabgrass family, for example, is difficult to kill, regenerates easily after pulling, and is resistant to chemicals and thermal trauma.
Many weeds such as crabgrass are fairly transparent to UV-C and the lethality of UV-B for short term applications of low energy is small in degree and not sufficient for a commercially successfully eradication method.
Now referring to FIGS. 6 and 7, there is depicted one typical class of prior art eradication processes or occurrences whereby extreme ultraviolet light induced trauma is delivered with a large UV radiative transfer via general illumination or flash onto a naturally grown species Digitaria sanguinalis rooted into a soil grade as shown. The radiation shown in FIG. 6 is shown for illustrative purposes, ranging from visible light, through UV-A, UV-B and UV-C and beyond, into what is known as Far Ultraviolet, extremely virulent and dangerous forms of radiation.
First, it should be noted that with the various protection mechanisms that plants employ, added amounts of UV radiation are quite often ineffective, either wholly or in practice, for a suitable process. When plants are normally in sunlight, they tend to develop a waxy layer on their leaves and other similarly exposed components. These plants tend to be resistant to UV radiation. In particular, monocots and dicots have protective cells, including a well-developed epidermis which comprises a waxy layer on top, called the cuticle. This waxy surface protects the leaves from sunburn, dessication (drying out) and reduces attacks by fungi, bacteria, virus particles and insects. This layer prevents what is called sunscald.
When moderate levels of UV radiation are used to attempt to clear nuisance vegetation, leaves can turn white in color as the radiation breaks down connections of layers, and as a result, the leaf is unable to conduct photosynthesis. However, the root structure remains, and the plant usually is able to adapt as after a forest fire, which inflicts similar damage.
Evaluating the effect of artificial illumination on nuisance plants can be complex, with competing and conflicting effects and factors. Prior art techniques have not been successful, overall. In many cases, added illumination in the form of general UV rays containing UV-A, UV-B and UV-C frequencies has been found to give benefits. Inconsistencies in prior art research findings are due to differing plant biology and genetics; soil conditions; and ambient light, e.g., shady versus sunny conditions.
There are many engineering considerations that figure importantly in determining the success of an eradication system using illumination. Among the many other factors in play when using artificial illumination to attempt eradication of nuisance plants are:
[1] Actual operative (beneficial versus detrimental) result from illumination stress
[2] Effectiveness, such as expressed lethality in percent dead after 30 days
[3] Total required input energy
[4] Time of Exposure and speed of operations
[5] UV-A levels, UV-B levels, UV-C levels
[6] Lamp and system complexity, cost, the need for controls, ballasts, and safety guards
[7] Operator and bystander safety, specifically often the UV exposure danger. This is a significant disadvantage for prior art methods such as that disclosed in U.S. Pat. No. 5,929,455 to Jensen, which discloses an eradication method using high energy radiation, high in UV-B and especially UV-C radiation, which is dangerous and mutating. Jensen '455 uses very high applied power.[8] Mutagenic effects from UV-B and UV-C to life forms at ground surface and into bulk soil. Although some mutagenic activity has been observed for even visible light, there is a steep exponential drop in mutagenic activity and effect for radiation over 320 nm wavelength.[8] Ignition hazard and lamp unit operating temperatures
A successful eradication system will develop and meet high benchmarks regarding these factors. While some effectiveness has been found using prior art methods, it has only been effective for very large and dangerous radiative transfers. The reason why these dangerous and very high energy transfers have been used is because prior art low energy methods have not worked.
The method described by Kaj Jensen in U.S. Pat. No. 5,929,455 uses an extremely high energy, dangerous process, specifically using UV-B and UV-C which have very high and special, qualitatively different, lethality. Interestingly, certain species such as crabgrass are fairly transparent to it for low dosages. Jensen '455 uses no other kind of light and employs a high pressure mercury (Hg) vapor lamp with a strong 254 nm UV-C emission line and no intervening phosphor. Such emissions, including similar emissions lines from other selected arc discharge lamps are very dangerous, expensive and require extensive controls and safeguards. Jensen '455 uses dosages very far greater than 10,000 joules per square meter merely to stop or retard growth dependent on the type and size of the plant. Actual lethality for a successful eradication process for the type of radiation Jensen '455 arrays is many tens of thousands of Joules per square meter exposure.
This type of high energy exposure of UV rays to kill life, including plant life, is known since at least the mid-20th century. During World War II and also during tests in decades after, it became known that certain high energy depositions of UV-B and UV-C radiation onto land kills vegetation—and it is energies in this regime, in terms of total Joules of deposited UV energy—that Jensen '455 uses.
The world's first hydrogen bomb test, conducted by the United States in the Bikini Atoll in March, 1954, had unprecedented explosive power, an equivalent explosive yield of as high as 15 Megatons of TNT (Trionitrotoluene). By contrast, the blasts at Hiroshima and Nagasaki in Japan in August, 1945 yielded an estimated 16,000 tons and 21,000 tons, respectively. Radiation effects from these blasts received very high attention and study.
According the Radiation Effects Research Foundation (RERF), a non-profit organization conducted in accord with an agreement between the governments of Japan and the United States, initial radiation effects were assessed by the Atomic Bomb Casualty Commission (ABCC) established in 1947, which was later re-organized into the RERF in 1975. This included extremely extensive and detailed epidemiological studies of health and longevity on more than 120,000 affected individuals, with research conducted for over fifty years. It also included detailed observations of effects on plants and animal life.
From the discoveries made after the bombing of Hiroshima and Nagasaki, regarding the effects on plant life from the measured emissions of electromagnetic (light) radiation, the application of a high amount of UV, including UV-A, UV-B and UV-C, to kill plants appears to be known. Generally, the energy of a typical atomic bomb is distributed roughly as 50% blast pressure, 35% as heat, and 15% as radiation (all types).
During the two atomic bomb blasts of 1945, the greatest number of radiation injuries was deemed to be due to ultraviolet rays. The origination of the ultraviolet rays comes from the extremely high temperature flash of the initial reaction in the detonated atomic bomb. These rays cause very severe flash burns and they were well known to have killed plant life. The radiation comes in two bursts: an extremely intense “flash” discharge lasting only 3 milliseconds, and a less intense one of longer duration, lasting several seconds. The second burst contains by far the larger fraction of total light energy, over ninety percent.
The first flash or discharge is especially rich in ultraviolet radiation, which is very biologically destructive. The total deposition energy of the initial flash alone is such that, with no time for heat dissipation, the temperature of a person's skin would have been raised 50 C by the flash of visible and ultraviolet rays in the first millisecond at a distance of just under 4000 meters from the blast zone.
This research was conducted by the Manhattan Atomic Bomb Investigating Group, formed on 11 Aug. 1945, two days after the bombing of Nagasaki, via a message from Major General Leslie R. Groves to Brigadier General Thomas F. Farrell. The biological effects of high amounts of UV radiation on plant life were especially obvious and pronounced by examining the aftermath of the first hydrogen bomb test on the Bikini Atoll.
Young naval officers on deck of the USS Bairoko witnessed, while in the Bikini Atoll about 50 km from the hydrogen bomb blast site, an intense flash followed by a longer radiation burst of some seconds duration, in turn followed by heavy, warm, blast-driven winds. The ultraviolet radiation from the flashes was sufficient to kill fish deep underwater, as evidenced by many varied fish floating to the surface, with bodies burned on one side or region, from incident UV rays. The ultraviolet radiation also killed plant life over a very large area. Various measurements were retained even though the blast destroyed many instruments that were set up in permanent buildings to measure it.
From the standpoint of acceptable lethality for a success eradication process, all low energy previous prior art techniques have fallen short and have not been acceptably effective. Speed of application and overall success rate are very important. Generally, the delivery of trauma which resembles natural trauma (e.g., severing, pulling, application of heat etc.) is not effective as bona fide reliable eradication methods, because the plants so treated tend to heal and regenerate, probably as a result of centuries of evolution. The delivery of illumination trauma in the low energy regime as attempted in the prior art is similarly not effective. Also, many prior art discoveries regarding application of artificial radiation to plants often exist ostensibly to serve another other objective, such as benefitting the plant, by removing pathogens or insects, etc.